1. Field of the Invention
The present invention relates generally to slotted hole screens which are suited for use in devices for separating or leaning aqueous fiber suspensions, in particular, for paper manufacturing.
2. Description of the Related Art
In the manufacture of paper, there are various steps that require the treatment of aqueous solutions, for example, removing or aligning fibers in the solution. This treatment is generally performed with slotted hole screens having wire-shaped or bar-shaped longitudinal members defining the screen slots. The longitudinal members are mounted on cross bars. These slotted hole screens are commonly referred to as xe2x80x9cwedgewire screens.xe2x80x9d An example of such a wedgewire screen is provided in U.S. Pat. No. 5,011,065, the disclosure of which is incorporated by reference in its entirety.
There are three principle methods for constructing wedgewire screens. The first method uses resistive welding. In this method, xe2x80x9cprofilatedxe2x80x9d wire, that is, wire having a predetermined profile, is pressed down and into a support ring by using a combination of high pressure and high current. This will cause the edge of the wire to melt into the support rings. The advantage of this method is that it is fast; however, there are significant shortcomings. For example, the weld is typically small and brittle. This makes the screen unsuitable for applications that involve significant pulsation and/or vibration. Inside a wedgewire screen for the pulp and paper industry, there normally is heavy pulsation and vibration. This causes a significant number of mechanical failures on the resistance welded portions of the slotted wire screens.
In addition, there may be a problem with plugging. Near the weld, there are usually a significant number of sharp burrs. These burrs may not be large, but they are usually large enough to cause fibers to stick to them. After some time, the fibers accumulate such that the screen will be plugged.
For the pulp and paper industry, it is desirable to have a certain angle at the top of the wire, and that angle may, to a certain degree, be achieved by tilting the wire. This is difficult to achieve in production. When pressure is added to the tilted wire during welding, the wire will, very often, have the tendency to tilt slightly more or slightly less than the desired angle. This will, of course, make the angle uneven, and the slot opening between the wires will vary accordingly.
The next most common method for forming slotted screens is Gas Tungsten Arc welding, or TIG welding, of the wires on the support rings. The advantage of this method is that the weld is bigger and stronger, and is more suitable for a pulsation and vibration environment. If the welding is performed properly, there will not be any burrs on the screens. Despite these advantages, the method is very slow. Further, a xe2x80x9ccombxe2x80x9d will have to be produced to act as a jig for the wire, so that the wire can be positioned with the desired angle and slot width. Thus, each size wedgewire screen will require its own jig, resulting in manufacturers maintaining a large number of jigs.
The third method involves the mechanical locking of wires to the support rings. An example of such is shown in U.S. Pat. No. 5,090,721, the disclosure of which is incorporated by reference in its entirety. In this example, the wire has a bulb on the backside, which fits into a precut groove in the support ring. When this screen is rolled into a cylinder, there will be significant pressure between the wires, which keeps the wires locked into the support ring. Although this may, for the most part, be a good solution; mechanical locking, however, does not work well on high-grade stainless steel. Higher grades of stainless steel have a tendency to stretch over time, especially under the application of continuous load.
A common problem with the aforementioned methods is that the screen is made in the form of a flat panel first, and that screen panel is then rolled up to the correct radius afterwards. This rolling process may create distortions in the slot width if the support ring is too strong. To avoid this problem, the support ring that is on the original flat panels is very small and weak; this is compensated for later by welding additional support rings to the original, smaller support rings. This creates significant shrink and stress in the material, and is also very time-consuming.
Some manufactures shrink extra support rings on the original support ring. This creates problems, however, because forces from the original support ring are generally not evenly transferred to the outer support ring.
Therefore, a need has arisen for an apparatus and method for forming slotted wire screen that overcomes these and other shortcomings.
According to one embodiment of the present invention, a method for forming a slotted wire screen is disclosed. The method involves the steps of (1) providing support ring material; (2) positioning a wire on the support ring material; (3) joining the wire and the support ring material; and (4) bending the support ring material to form a ring of a radius. The steps of joining and bending may be performed at substantially the same time.
According to another embodiment of the present invention, a method for forming a slotted wire screen is disclosed. The method involves the steps of (1) providing support ring material; (2) providing the support ring material with a brazing compound; (3) positioning a profilated wire on the support ring material; (4) passing the support ring material and the positioned profilated wire through a heating zone; and (5) cooling the profilated wire and support ring material. In the heating zone, the profilated wire and the support ring material are brazed by the heat, and, at substantially the same time, the support ring material is bent to form a ring.
According to another embodiment of the present invention, an apparatus for forming a slotted wire screen is disclosed. The apparatus includes a device for pushing support ring material; a device for providing the support ring material with an adhesive, such as a brazing compound; a device for positioning a wire on the support ring material; a heating zone for heating the support ring material and the wire; and a device for bending the support ring material.
According to another embodiment of the present invention, a method for forming a slotted wire screen is disclosed. The method includes the steps of (1) providing a cage material, the cage material comprising at least one piece of support ring material and at least one piece of wire joined to the support ring material; and (2) bending the cage material to form a ring of a radius. The bending may be performed by at least one arm or at least one roller. The cage material may include support ring material and profilated wire that are prejoined and preformed.
A technical advantage of the present invention is that an apparatus and method for forming slotted wire screens is disclosed. Another technical advantage of the present invention is that the connection between the profilated wire and the support ring is large, making the screen sturdy and strong. Another technical advantage is that there are no burrs formed in the brazing process. Yet another technical advantage of the present invention is that the screen will be practically free from internal stresses due to the very high temperature used for brazing and bending. Another technical advantage of the present invention is that, because two operations are performed at the same time, it is very cost effective. Another technical advantage of the present invention is that because no force is added to the profilated wires during roll up or later, the high precision of the slotted screen is preserved.